Objective lens

Details Objective lens Objective lens

1999-07-01

2001-05-29

Epps, Georgia (Department: 2873)

Optical: systems and elements

Lens

With light limiting or controlling means

C359S740000, C359S016000, C359S822000

Reexamination Certificate

active

06239922

ABSTRACT:

BACKGROUND OF THE INVENTION
An endoscope is inserted into narrow spaces such as human internal body parts or the interior of an engine. Therefore it is desirable that the outer diameter of an endoscope be as small as possible, and this requires that the diameter of the lens that is arranged at the tip of an endoscope be as small as possible. An example of a lens of an endoscope that has a comparatively small diameter and wherein the lens is made using only a few lens elements is described in Japanese Laid-Open Patent Applications H9-68647 and H7-84179.
FIG. 9
illustrates the same objective lens element structure as that of Example 1 of Japanese Laid-Open Patent Application H9-68647, but includes different labels and, in addition to showing the objective lens elements themselves,
FIG. 9
also illustrates conjectured support structure and flare-reducing structure for these lens elements. The lens comprises, in order from the object side, a first lens element lens L
1
, an aperture stop
5
(ie., a brightness diaphragm), a second lens element L
2
of positive refractive power and a third lens element L
3
of positive refractive power. In one embodiment of Japanese Laid-Open Patent Application H9-68647, lens element L
1
, which in all other embodiments is piano-concave, is replaced by a plane-parallel cover plate. Although no support structure whatsoever for these lens elements is actually shown in Japanese Laid-Open Patent Application H9-68647,
FIG. 9
illustrates the assumed support structure for these components based on standard practices in the art, as will now be discussed. Because the first lens element L
1
(or cover plate, as the case may be) and the second lens element L
2
have the same outer diameter, they have been illustrated in
FIG. 9
as being fixed to a first support frame SF
1
. An aperture stop
5
lies between the first lens element L
1
and the second lens element L
2
. Thus, the first support frame SF
1
, is shown supporting these three elements. Further, it is likely that the outer diameter of the first support frame SF
1
would be sized to equal the outer diameter of the third lens element L
3
, which in Japanese Laid-Open Patent Application H9-68647 is shown as having an outer diameter that is slightly larger than the outer diameter of the other two lens elements. Having their outer diameters equal would enable the first support frame SF
1
and the second lens element L
2
to each be inserted into a second support frame SF
2
, as illustrated in FIG.
9
. Adjacent lens element L
3
in
FIG. 9
is illustrated a conjectured flare diaphragm
7
and a diaphragm receiving member
8
, as would commonly be used in the prior art to form a flare stop.
FIG. 10
illustrates the lens element structure of Example 6 of Japanese Laid Open Patent Application H7-84179. The lens of this example includes, in order from the object side, a plano-concave lens L
1
, an aperture stop
5
, a positive meniscus lens element L
2
, and a positive lens element L
3
.
In image formation lenses generally, in order to remove the light which does not contribute to image formation, a flare stop is often provided. There is no known description in the above-mentioned two patents which relates to a flare stop. However, as shown in prior art
FIG. 9
for optical diaphragms generally, a flare diaphragm
7
and a diaphragm receiving member
8
are often provided on the object side of lens element L
3
. In many cases, such a flare stop is provided at this position in order to prevent stray light that has been reflected off the inner surface of the frame from passing through to the observer. The flare stop is positioned before lens element L
3
because stray light rays (i.e., those from a larger angle of view than for which the lens was designed to image) in many cases are incident on the frame between positive lens elements L
2
and L
3
.
However, if the outer diameter of a lens element is made smaller to achieve size reduction, the associated diaphragm receiving member and flare stop member must also be made smaller. Because these members are each shaped as an annular ring which circumscribes an aperture having a diameter that is nearly the same diameter as the lens element itself, as the lens element becomes smaller, the width of the annular ring becomes so small that manufacture and assembly of the ring become difficult.
Although it is known to bevel the edge of a lens element so as to form a sloped surface near the circumference of the lens element and to use this surface to self-center a lens element in lieu of using a spacer ring (as taught, for example, in U.S. Pat. No. 5,589,989) there is no teaching in this reference or any other reference known to applicant which suggests beveling an edge of a lens element and applying a light shielding material (i.e., one which absorbs or attenuates light) to a sloped surface created by the beveling process in order to reduce flare. Nor is there any suggestion that such an approach to reducing flare will result in fewer components and result in an overall cost reduction for assembling a lens system having small diameter components.
BRIEF SUMMARY OF THE INVENTION
The present invention forms an inclined or sloped surface on an optical member (such as a lens element, plane-parallel plate of a filter or cover glass, etc.), near the outer diameter of the optical member and applies a light shielding substance to the sloped surface in order to achieve flare reduction. The sloped or inclined surface, which may be the lens element surface itself, is immediately adjacent a circumferential edge of the optical element, and the circumferential edge is supported by a holding member. Alternatively, the present invention omits forming a separate, planar, sloped surface for the light shield, and instead designs the optical member so a light shielding substance may be easily applied to a sloped surface of a convex lens element near its periphery in order to shield flare from reaching the image. Flare, as used herein, refers to unwanted light which enters an optical system outside the intended field of view and is reflected toward the image plane by one or more surfaces of the optical system. A first object of the invention is to avoid using an annular ring for flare reduction in the case where the diameter of the optical member is small A second object of the invention is to enable the overall manufacturing and assembly cost of an optical system to be reduced by achieving the first object of the invention, while still maintaining adequate flare reduction. Thus, the present invention relates particularly to very small optical members, such as lens elements, filters or cover plates as may be found in endoscopes, or in other applications (e.g., in small electronic cameras, small cameras for monitoring, etc.) where size reduction causes the prior art structures and methods for flare reduction (discussed above) to become unsatisfactory.


REFERENCES:
patent: 5589989 (1996-12-01), Estelle et al.
patent: 5675445 (1997-10-01), Uemara
patent: 5801889 (1998-09-01), Meyers
patent: 7-84179 (1995-03-01), None
patent: 9-68647 (1997-03-01), None

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